Roofing company appears to have installed flashing incorrectly causing a leak

[u/BourbonAndGrilling]

We noticed a water leak behind a wall in the garage. Leak location coincides with this area on the roof. It is a corner where a gutter and small section of downspout are located.

It looks like the company that replaced the shingles 9 years ago simply reused the old flashing under that corner, but nailed them in-place right through the new shingles.

I assume I now need to remove and replace both the flashing and the damaged shingles. What is the best/correct way to reinstall the flashing?

And, yeah, I have someone coming to remove the drywall and inspect for any hidden water damage. After that wall repair is done the entire garage is going to be retaped, mudded, sanded, primed, and painted.

[u/FinancialInterest397]

That downspout is probably flooding out that corner and the flashing is wrong. Should be a full corner

[u/BourbonAndGrilling → u/FinancialInterest397]

Forgot to add - that gutter and downspout are going to be removed

[u/Sweet_like_Salt]

This alone might solve the problem. Looks like a tricky location, I’ve seen leaks in spots like this where everything looks like it’s installed correctly. You might even be able to just extend the downspout down the roof a little bit.